>>>>> Gebhardt, Albrecht <albrecht.gebha...@aau.at> >>>>> on Sun, 19 Mar 2017 09:14:56 +0000 writes:
> Hi, > the function outer can not apply a constant function as in the last line of the following example: >> xg <- 1:4 >> yg <- 1:4 >> fxyg <- outer(xg, yg, function(x,y) x*y) >> fconstg <- outer(xg, yg, function(x,y) 1.0) > Error in outer(xg, yg, function(x, y) 1) : > dims [product 16] do not match the length of object [1] > Of course there are simpler ways to construct a constant matrix, that is not my point. > It happens for me in the context of generating matrices of partial derivatives, and if on of these partial derivatives happens to be constant it fails. > So e.g this works: > library(Deriv) > f <- function(x,y) (x-1.5)*(y-1)*(x-1.8)+(y-1.9)^2*(x-1.1)^3 > fx <- Deriv(f,"x") > fy <- Deriv(f,"y") > fxy <- Deriv(Deriv(f,"y"),"x") > fxx <- Deriv(Deriv(f,"x"),"x") > fyy <- Deriv(Deriv(f,"y"),"y") > fg <- outer(xg,yg,f) > fxg <- outer(xg,yg,fx) > fyg <- outer(xg,yg,fy) > fxyg <- outer(xg,yg,fxy) > fxxg <- outer(xg,yg,fxx) > fyyg <- outer(xg,yg,fyy) > And with > f <- function(x,y) x+y > it stops working. Of course I can manually fix this for that special case, but thats not my point. I simply thought "outer" should be able to handle constant functions. ?outer clearly states that FUN needs to be vectorized but function(x,y) 1 is not. It is easy to solve by wrapping the function in Vectorize(.): > x <- 1:3; y <- 1:4 > outer(x,y, function(x,y) 1) Error in dim(robj) <- c(dX, dY) : dims [product 12] do not match the length of object [1] > outer(x,y, Vectorize(function(x,y) 1)) [,1] [,2] [,3] [,4] [1,] 1 1 1 1 [2,] 1 1 1 1 [3,] 1 1 1 1 ---------------- So, your "should" above must be read in the sense "It really would be convenient here and correspond to other "recycling" behavior of R" and I agree with that, having experienced the same inconvenience as you several times in the past. outer() being a nice R-level function (i.e., no C speed up) makes it easy to improve: Adding something like the line if(length(robj) == 1L) robj <- rep.int(robj, dX*dY) before dim(robj) <- c(dX, dY) [which gave the error] would solve the issue and not cost much (in the cases it is unneeded). Or is this a bad idea? ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel